Study on Rules and Mechanism of Layer Thickness Variation in Stratified Rock Slope

• 1、School of Civil Engineering and Mechanics，Lanzhou University，Lanzhou，Gansu 730000，China

Abstract：IFirstly, the slope of stratified rock mass of a hydropower station in the upper reachesof the Yellow River was takenas an object, and the spatial variation laws of layer thickness ofmetamorphic sandstones and slatewas revealed through field measurementin 90 adits and on the ground.Then, combining with the geological environment and its evolution, the influencing factors and the influence scope of layer thinning were analyzed.Finally, based on in-situ stress measurements, rock mass wave velocity tests, stress-elastic wave coupling triaxial tests and numerical simulations, the mechanism of layer thinning in steeply inclined stratified rock mass slopes under unloading conditions was researched.The combined effects of lithology, geotectonic movement, unloading, and weathering lead to the thinning of rock layer.The soft-hard interbedded rock mass and their potential weak planes are the foundationof thelayer thinning. The geotectonic movements make the potential weak planesto shear andthen the action of unloadingdrives the surfaces to open into cracks. Afterwards, the action of weathering causes the shallow rocks further thinning.River incisionmakes the stress field in the rock slope very complicated, which leads to the potential weak planes within the slopecrest and the slope develop into tension cracks. Meanwhile, the compression fracture along the potential weak planes also happenedwithin a certain depth range of the slope, and thenlayer thinning occurred in a wide range of the steeply stratified rock slope.As a result, the thickness of layer in the stratified rock mass generally increases oscillatingly with depth,andit will tend to stable values where the thickness reaches the thickness of theoriginalstrata.Moreover, the layer thickness near the bedding fault zone, in the fold belts, and near the unloading crack belts are generally thinnerbut alsorise with the increase of burial depth. The layerthickness and its influence range increase with increasing elevation,andit is greaterin the anti-dip stratum in the left flank than in the right flank.In addition, there is a positive correlation among layer thickness, depth of burial, p-wave velocity and geo-stress, which indicates that the layer thickness is always influenced by in-situ stress state.This research can providesreferences for the study of mechanical properties and deformation failure and for the design of rock engineeringin the stratified rock mass.

Keywords： geological engineering stratified rock mass layer thickness of rock layer thinning of rock geo-stress field unloading